1. Field of the Invention
The present invention relates to a varnish composition, more particularly to a varnish composition for manufacturing pre-impregnated materials with improved and balanced physical characteristics.
2. Description of Related Art
Modern Printed Circuit Boards (PCB) are often made by laminating and curing/hardening pre-preg (pre-impregnated) materials, copper clad laminates (CCL), or copper films. Pre-impregnated materials (pre-pregs) are reinforcement fibers or fabrics impregnated with pre-catalyzed resin system. For example, one common way of pre-preg manufacture is by dipping glass fabrics into a varnish composition and then curing/hardening the fabrics to form thin layered prepreg. These reinforced composite fabric materials are suitable and widely applied to many different fields of technology, one of which is the manufacture of PCBs, due to their thinness, light-weight, and high mechanical strength. However, as the environmental protection laws become more and more restricted (such as RoHS, WEEE), lead-containing soldering materials are gradually required to be phased out in favor of lead-free counterparts for electronic application of all ranges. As the processing temperature for the lead-free soldering materials is in general 30 to 40° C. higher than that of the lead-containing solder, it is necessary to improve the heat-resisting property of the pre-preg material to improve its suitability for PCBs applications.
Furthermore, for environmental protection reasons, tighter regulations gradually forbid the use of widely used yet poisonous halogen-containing materials as flame retardants. In replacement, halogen-free PCB is widely used in electronic products. To compensate for the absence of halogen-based flame retardants, phosphorus or phosphorus-containing molecules or compounds are added to pre-preg materials to enhance the anti-flammability/fire-retardancy of the PCB. Traditionally, the varnish composition can contain either a primary resin having a phosphorus-containing compound or a hardener containing a phosphorus-containing compound. Alternatively, a phosphorus-containing compound may be separately added into the varnish composition to improve the anti-flammability of the PCB.
Moreover, as being widely used in various applications, the physical and chemical characteristics of modern pre-preg materials, such as the vitrification/glass transition temperatures (Tg), heat-resisting/anti-flaming characteristics, and moisture absorption properties, is preferable to possess better flexibility and adaptability to meet various specifications. Furthermore, for the application in PCB manufacturing, the varnish composition is required to have high machinability when subjected to drilling or other mechanical processing procedures. Therefore, the present disclosure provides a varnish composition suitable for manufacturing pre-preg composite and substrate thereof having more balanced and beneficial properties that can meet the requirement of a wide range of applications.
Therefore, in view of these difficulties, the inventor has developed ways to overcome these difficulties to provide a dependable product with reliable results in production; the present invention addresses these difficulties and allows reliable production at high speed and overcomes the above problems.